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ISCSI Target Vs ISCSI Initiator - Device Mapper Multipath

ISCSI - Provide block level storage access through IP Address.
Client Called (ISCSI- Initiator)   ISCSI Storage Devices (Targets) remote server.
IQN – ISCSI Qualified Name – iqn.2014-06.local.labs.infra:disk

1.#yum install iscsi-target-utils
2.Vim /etc/tgt/target.conf
<target iqn.2014-06.local.labs.infra:disk1>
                 backing –store /dev/sdb
<target iqn.2014-06.local.labs.infra:disk2>
                Backing-storge /dev/sdc
Iqn – iscsi Qualified Name
3. /etc/init.d/tgtd start
4.# tgt-admin -s (List out the LUN)
#iscsiadm –m discoverdb –t sendtargets –portal ISCSITARGETIP:3260 –discover,1 iqn.2013-03.local.labs.infra:disk1,1 iqn.2013-03.local.labs.infra:disk2
2) Login to the ISCSI TARGET
#iscsiadm –m node –portal ISCSITARGETIP:3260 –T iqn.2013-03.local.labs.infra:disk1 –l
# iscsiadm -m node –portal ISCSITARGETIP:3260 –T iqn.2013-03.local.labs.infra:disk2 –l
3) After iscsi login,it will list out list of devices client system.
#fidsk -l (Actually it has only two device due to the two physical network it will show four devices - 2 disk * 2 Physical network = 4 devices)
Disk /dev/sdb: 2147 MB, 2147483648 bytes
Disk /dev/sdc: 2147 MB, 2147483648 bytes
Disk /dev/sdd: 2147 MB, 2147483648 bytes
Disk /dev/sde: 2147 MB, 2147483648 bytes

1)DM-Multipath – More than one path  to the shared Storage.
2)Ability of the server communicate with same physical (or) logical storage block device across MULTIPLE PHYSCIAL path between HOST BUS ADAPTER in the server and STORAGE CONTROLLER for the device. Typically Fiber channel (or) ISCSI in SAN environment.
3)Why Multipath : Avoid single point of failure(Redundancy) and load balancing.
    HBA failure(2 HBA)
    FC cable failure(2 FC cable)
    SAN switch failure(2 SAN Switch)
    Array controller port failure
Real Time - Storage Multipath Configuration.
1)Each server has 2 FC Adapter
2)Have Two SAN Switch
3)Storage Controller have 4 FC Adapter

 With DM-Multipath configured, a failure at any of these points will cause DM-Multipath to switch to the alternate I/O path.
3)/etc/multipath.conf Configuration file creation
# cp /usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf /etc/
#cat /etc/multipath.conf.
prio alua to change const like.
defaults {
        udev_dir                /dev
        polling_interval        10
        path_selector           "round-robin 0"
        path_grouping_policy    multibus
        getuid_callout          "/lib/udev/scsi_id --whitelisted --device=/dev/%n --replace-whitespace"
        prio                    const
        path_checker            readsector0
        rr_min_io               100
        max_fds                 8192
        rr_weight               priorities
        failback                immediate
        no_path_retry           fail
        user_friendly_names     no
4)# /etc/init.d/multipathd restart
# ls -l /dev/mapper/* /dev/dm-*
brw-rw---- 1 root disk 253,  0 Jun 24 14:58 /dev/dm-0
brw-rw---- 1 root disk 253,  2 Jun 24 14:37 /dev/dm-1
lrwxrwxrwx 1 root root       7 Jun 24 14:37 /dev/mapper/1IET_00010001 -> ../dm-1 lrwxrwxrwx 1 root root       7 Jun 24 14:37 /dev/mapper/1IET_00020001 -> ../dm-0 crw-rw---- 1 root root  10, 58 Jun 24 12:30 /dev/mapper/control

Error & Solution
# iscsiadm -m discoverydb -t st --portal --discover
iscsiadm: cannot make connection to No route to host
iscsiadm: cannot make connection to No route to host
SOLUTION: Add The Input chain 3260 as ACCEPT in iptables.
#iptables -I INPUT -p tcp --dport 3260 -j ACCEPT.
Then the problem got solved.

TO ISCSI Configuration In EMC Storage Refer This PDF LINK.

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